In a statement, Deloitte Tax says it stands “fully behind the services our team provided” and plans a vigorous defense.

Davidson died in 2009 at age 86. He owned Auburn Hills-based Guardian Industries, an auto industry glass products supplier.

The estate in July agreed to pay the IRS $388 million to settle the $2.8 billion claim, which was made in 2013. It says Davidson’s accountants undervalued privately held Guardian stock placed in trusts for his family.